mac80211: minstrel_ht: add flag to indicate missing/inaccurate tx A-MPDU length

Some hardware (e.g. MediaTek MT7603) cannot report A-MPDU length in tx status
information. Add support for a flag to indicate that, to allow minstrel_ht
to use a fixed value in its internal calculation (which gives better results
than just defaulting to 1).
Signed-off-by: Felix Fietkau <nbd@nbd.name>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>

include/net/mac80211.h

@@ -2190,6 +2190,9 @@ struct ieee80211_txq {
  *	MMPDUs on station interfaces. This of course requires the driver to use
  *	TXQs to start with.
  *
+ * @IEEE80211_HW_TX_STATUS_NO_AMPDU_LEN: Driver does not report accurate A-MPDU
+ *	length in tx status information
+ *
  * @NUM_IEEE80211_HW_FLAGS: number of hardware flags, used for sizing arrays
  */
 enum ieee80211_hw_flags {
@@ -2238,6 +2241,7 @@ enum ieee80211_hw_flags {
 	IEEE80211_HW_BUFF_MMPDU_TXQ,
 	IEEE80211_HW_SUPPORTS_VHT_EXT_NSS_BW,
 	IEEE80211_HW_STA_MMPDU_TXQ,
+	IEEE80211_HW_TX_STATUS_NO_AMPDU_LEN,
 
 	/* keep last, obviously */
 	NUM_IEEE80211_HW_FLAGS

net/mac80211/debugfs.c

@@ -218,6 +218,7 @@ static const char *hw_flag_names[] = {
 	FLAG(BUFF_MMPDU_TXQ),
 	FLAG(SUPPORTS_VHT_EXT_NSS_BW),
 	FLAG(STA_MMPDU_TXQ),
+	FLAG(TX_STATUS_NO_AMPDU_LEN),
 #undef FLAG
 };
 

net/mac80211/rc80211_minstrel_ht.c

@@ -294,6 +294,15 @@ minstrel_get_ratestats(struct minstrel_ht_sta *mi, int index)
 	return &mi->groups[index / MCS_GROUP_RATES].rates[index % MCS_GROUP_RATES];
 }
 
+static unsigned int
+minstrel_ht_avg_ampdu_len(struct minstrel_ht_sta *mi)
+{
+	if (!mi->avg_ampdu_len)
+		return AVG_AMPDU_SIZE;
+
+	return MINSTREL_TRUNC(mi->avg_ampdu_len);
+}
+
 /*
  * Return current throughput based on the average A-MPDU length, taking into
  * account the expected number of retransmissions and their expected length
@@ -309,7 +318,7 @@ minstrel_ht_get_tp_avg(struct minstrel_ht_sta *mi, int group, int rate,
 		return 0;
 
 	if (group != MINSTREL_CCK_GROUP)
-		nsecs = 1000 * mi->overhead / MINSTREL_TRUNC(mi->avg_ampdu_len);
+		nsecs = 1000 * mi->overhead / minstrel_ht_avg_ampdu_len(mi);
 
 	nsecs += minstrel_mcs_groups[group].duration[rate] <<
 		 minstrel_mcs_groups[group].shift;
@@ -503,8 +512,12 @@ minstrel_ht_update_stats(struct minstrel_priv *mp, struct minstrel_ht_sta *mi)
 	u16 tmp_cck_tp_rate[MAX_THR_RATES], index;
 
 	if (mi->ampdu_packets > 0) {
+		if (!ieee80211_hw_check(mp->hw, TX_STATUS_NO_AMPDU_LEN))
 			mi->avg_ampdu_len = minstrel_ewma(mi->avg_ampdu_len,
-			MINSTREL_FRAC(mi->ampdu_len, mi->ampdu_packets), EWMA_LEVEL);
+				MINSTREL_FRAC(mi->ampdu_len, mi->ampdu_packets),
+					      EWMA_LEVEL);
+		else
+			mi->avg_ampdu_len = 0;
 		mi->ampdu_len = 0;
 		mi->ampdu_packets = 0;
 	}
@@ -709,7 +722,9 @@ minstrel_ht_tx_status(void *priv, struct ieee80211_supported_band *sband,
 	mi->ampdu_len += info->status.ampdu_len;
 
 	if (!mi->sample_wait && !mi->sample_tries && mi->sample_count > 0) {
-		mi->sample_wait = 16 + 2 * MINSTREL_TRUNC(mi->avg_ampdu_len);
+		int avg_ampdu_len = minstrel_ht_avg_ampdu_len(mi);
+
+		mi->sample_wait = 16 + 2 * avg_ampdu_len;
 		mi->sample_tries = 1;
 		mi->sample_count--;
 	}
@@ -777,7 +792,7 @@ minstrel_calc_retransmit(struct minstrel_priv *mp, struct minstrel_ht_sta *mi,
 	unsigned int cw = mp->cw_min;
 	unsigned int ctime = 0;
 	unsigned int t_slot = 9; /* FIXME */
-	unsigned int ampdu_len = MINSTREL_TRUNC(mi->avg_ampdu_len);
+	unsigned int ampdu_len = minstrel_ht_avg_ampdu_len(mi);
 	unsigned int overhead = 0, overhead_rtscts = 0;
 
 	mrs = minstrel_get_ratestats(mi, index);

net/mac80211/rc80211_minstrel_ht_debugfs.c

@@ -160,6 +160,7 @@ minstrel_ht_stats_open(struct inode *inode, struct file *file)
 			"lookaround %d\n",
 			max(0, (int) mi->total_packets - (int) mi->sample_packets),
 			mi->sample_packets);
+	if (mi->avg_ampdu_len)
 		p += sprintf(p, "Average # of aggregated frames per A-MPDU: %d.%d\n",
 			MINSTREL_TRUNC(mi->avg_ampdu_len),
 			MINSTREL_TRUNC(mi->avg_ampdu_len * 10) % 10);